Within a rolling process for flat or long products, the need to measure the speed of the product at exit from a rolling stand is known.
Various solutions have been proposed for this purpose, but these have often proved, for various reasons, unsuitable and/or not completely effective.
In particular, methods involving contact are known, for example based on measuring rolls, which are unadvisable given the high temperatures of the rolled metal products in the rolling line, giving rise to problems of slipping, cooling and wear which lead to a reduction in the accuracy of the measurements.
Doppler effect laser measurers are also known, and therefore without contact, but these are costly and complex and, for low or negative speeds, need expensive acoustic-optical modulators.
Moreover, these laser measurers are not suitable for applications dedicated to small section rolled products, which are subject to vibrations or oscillations transverse to the direction of feed, with displacements with respect to the direction of feed of an entity comparable to or greater than the section size of the rolled product itself.
Indeed, in such cases, the use of laser, which produces a substantially dot-like beam of coherent light which hits the rolled product, does not guarantee, in the event of oscillations as above, that the measuring device is constantly trained, which leads to inaccuracies or failure in the measurement of speed.
Furthermore, in the case of small diameter round rolled products of the ribbed type, suitable for structural applications in making reinforced concrete structures, neither the solution with the contact measuring roll nor the Doppler effect laser measurer provide acceptable results, because of the particular structure of the surface of the rolled product.
Document U.S. Pat. No. 3,824,015 describes a method and the relative apparatus for the optical measurement of a moving product, such as a rolled metal product, which provides to use two means to detect a ray of light coming from the product and mounted distanced on a support structure, which detect light signals in a temporally delayed manner one from the others, so as to form an image of the surface of the element of the product on each detection mean, and to generate a corresponding correlation function according to which the value of speed of the product can be calculated.
Document U.S. Pat. No. 4,912,519 describes an apparatus for measuring speed comprising a semiconductor laser to irradiate light on a moving object and two photo-sensor devices, disposed in the direction of movement of the objects at a predetermined distance from each other and temporally delayed one with respect to the other so as to calculate the speed or the distance traveled in time by the object.
Document US-A-2001/0046042 describes a device for measuring the speed of an object that comprises two sensors disposed distanced along the direction of movement of the object, and which transmit the relative signals to a delay correlation device which digitalizes the signals, calculates the time stagger of the signals and carries out a phase comparison of the digitalized instantaneous values from which the speed is found.
Document DE-A-4225842 describes a device for measuring the speed of fabrics which comprises two optical or capacitive sensors distanced from each other and a time correlation device.
Document EP-A-0.065.906 describes a correlation device and method to determine the speed of a moving product.
One purpose of the present invention is to achieve a device for measuring the speed of moving products, in particular but not only rolled metal products in a rolling line, and to perfect a relative measuring method, which is without contact, economical, reliable and accurate.
Another purpose of the invention is to achieve a speed measuring device, and to perfect a relative method, suitable for contexts where there are rolled products, also with a limited section, subject to vibrations or oscillations transverse to the direction of feed, also big vibrations or oscillations, in any case maintaining high measurement precision and reliability.
A further purpose of the present invention is to achieve a speed measuring device and to perfect a relative method, suitable to measure the speed of bars or other rolled products, of the ribbed type.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.